This invention concerns linear recording media such as magnetic tape, and especially those media that exhibit diminished performance due to dimensional instability.
Modern data storage systems use servopositioning (or xe2x80x9cservoxe2x80x9d) systems to guide their recording and playback components with respect to a recording medium, and thus enable high track density, which increases data storage capacity. Errors in the ability to follow the servopositioning signals on the medium can cause unacceptable reductions in storage capacity, recording/playback rates, and other parameters that are important to consumers (and thus to system manufacturers).
Dimensional changes in magnetic recording media caused by variations in stress state or environmental conditions represent major obstacles towards recording trackwidth reduction, especially in flexible media. For example, estimates for reduction and control of media dimensional changes suggest improvement by a factor of two for future generations of magnetic media based on flexible PET or PEN substrates. Modifications to the recording system will also be required to mitigate the limitations of substrate instability. The trend towards even larger numbers of parallel channels exacerbates the effects of medium dimensional instabilities.
U.S. Pat. No. 6,222,698 (Barndt et al.) discloses an approach in which the entire multi-transducer magnetic head assembly is tilted at an azimuth angle relative to the magnetic tape to compensate for variations in tape width due to sources of dimensional instability, such as age-related tape shrinkage.
The invention provides methods and systems for reducing effects of dimensional instability of recording media having prerecorded servopositioning tracks.
One specific aspect of the invention is a method of reducing effects of dimensional instability of a recording medium, comprising separating multiple channels on a recording head into m groups of head channels, and independently positioning each group of heads relative to pre-written servo tracks on the medium.
In another aspect, the invention is a method of reducing effects of dimensional instability of a recording medium, comprising separating n channels on a recording head into m groups of channels, each group comprising at least one servo read head, and independently positioning each group of heads relative to pre-written servo tracks on the medium to minimize track misregistration caused by tape width variation. In this aspect, the track misregistration, TM, equals (n/m) times P times xcex94, where P is the head channel pitch, and xcex94 is fractional change in transverse dimension.
In another aspect, the invention is a method in which a recording head comprises groups of heads spaced apart from each other. An actuator for each pair of adjacent groups adjusts the relative spacing of at least one member of the pair with respect to the other member of the pair (i.e., one of the members could be stationary, or both members could be movable). A position error signal (PES) is measured in a conventional manner and the actuator is used to adjust the spacing of the groups to reduce the PES of each individual group. In the most preferred embodiment, there are two groups of heads, but in general there could be more. A specific implementation of this aspect includes at least the following steps: first providing the medium with at least one pair of pre-written servo tracks separated by a servo track spacing distance; providing a recording head assembly comprising at least one data head, and a pair of servo read heads spaced from each other by an amount nominally equal to the servo track spacing distance; providing the recording head assembly with an actuator to adjust the location, relative to the medium, of the pair of servo read heads; measuring, with the servo read heads from the pre-written servo tracks, a position error signal (PES) representative of the dimensional changes of the recording medium; and reducing the PES by adjusting transverse separation between any two servo read heads relative to the medium.